The invention is directed to apparatus and methods for applying liquid materials to a web and further processing the web by application of additional liquid material to the web through an electrostatic field.
Conventional web-offset printing presses utilize heat-settable ink that is set or cured by heat after the ink is printed onto a paper web. The curing of the ink is typically done by passing the web through a dryer, which causes the temperature of the web to be raised to a relatively high temperature, such as in the range of 250xc2x0 to 320xc2x0 F. (Fahrenheit). After it passes from the dryer, the hot web must be cooled to allow effective processing of the web in subsequent operations.
FIG. 1 schematically illustrates a prior art web-offset printing press 10 of the type described generally above. Referring to FIG. 1, the prior art printing press 10 incorporates a plurality of rotatable printing cylinders 12, 14, each of which applies an image to a paper web 16 using a heat-settable ink. The paper web 16, which is guided by a number of rollers 18, passes through the printing press 10 from left to right, as indicated by the arrow shown in FIG. 1.
After the ink is applied by the printing cylinders 12, 14, the web 16 is passed through a dryer 20, which sets the ink by raising the temperature of the web 16 to a relatively high temperature. After passing through the dryer 20, the web 16 is passed over a plurality of chill rolls 22 to cool the web 16. Heat from the web 16 is absorbed by relatively cool water which is piped through the chill rolls 22. After passing through all of the chill rolls 22, the web 16 is at or close to (within 10xc2x0 F.) room temperature.
After being heated by the dryer 20 and cooled by the chill rolls 22, the paper web 16 has very little moisture content. Consequently, after being cooled by the chill rolls 22, the web 16 is fed to an electrostatic remoistener 24 which adds moisture back to the web 16. The remoistener 24 is provided with a plurality of spray nozzles (not shown) for spraying water droplets onto the paper web 16 and a plurality of field directors (not shown) on each side of the web 16 for generating a directed electrostatic field. The field directors on one side of the web 16 are maintained at a high voltage relative to the field directors on the other side of the web 16, and water is sprayed through the electrostatic field so that the water droplets travel within a confined path between the spray nozzles and the paper web 16.
The invention is directed to an apparatus for processing a web of material by applying a liquid material to the web, heating the web, cooling the web and moistening the web. The apparatus includes an applicator that applies the liquid material to the web, a drying apparatus that heat-s the web to an initial temperature of greater than about 250xc2x0 F. and causes the web to have a moisture content of no greater than about 1.5%, a first cooling apparatus that causes the initial temperature of the web to be reduced to a second temperature no greater than about 210xc2x0 F. and no less than about 100xc2x0 F., a moistening apparatus that causes the moisture content of the web to be increased to at least about 2.5%, and a second cooling apparatus that causes the web to be cooled to a temperature not greater than about 100xc2x0 F. The moistening apparatus includes a generator adapted to generate a directed electrostatic field through which the web passes and a sprayer adapted to spray liquid through the electrostatic field and onto the web when the temperature of the web is between about 210xc2x0 F. and 100xc2x0 F.
The electrostatic field generator may be composed of a plurality of first field directors disposed on a first side of the web, each of the first field directors having a plurality of electrodes, a plurality of second field directors disposed on a second side of the web opposite the first side, each of the second field directors having a plurality of electrodes, and a voltage supply that supplies a relatively high voltage to the electrodes of one of the first or second field directors.
The invention is also directed to a method of processing a web that includes the steps of: (a) applying a liquid material to the web, (b) heating the web to a temperature of at least about 250xc2x0 F. and to cause the web to have a moisture content of no greater than about 1.5%, (c) cooling the web to a temperature of no greater than about 210xc2x0 F. and no less than about 100xc2x0 F., (d) generating a directed electrostatic field, (e) causing the web to pass through the directed electrostatic field, (f) spraying liquid through the directed electrostatic field and onto the web when the web has a temperature of between about 210xc2x0 F. and 100xc2x0 F. to cause the web to have an increased moisture content of at least about 2.5%, and (g) further cooling the web to cause the web to have a temperature of no greater than about 100xc2x0 F.
In the above apparatus and method, the liquid material may be applied evenly to the web by an applicator to create a substantially uniform coating of the liquid material on the web, or alternatively, the liquid material may be applied as ink by a plurality of printing cylinders of a printing press.
The features and advantages of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiment, which is made with reference to the drawings, a brief description of which is provided below.